1. Field of the Invention
This invention relates to the field of networking. In particular, the invention relates to communicating data within measurement traffic.
2. Description of the Related Art
Internetworks such as the Internet provide a best-effort service and do not reserve resources for a path. Hence, performance characteristics of the path such as delay, jitter and loss can change over time due to routing changes, congestion, and lack of connectivity, and therefore it is important to being able to measure them. There are several tools available to measure the performance characteristics of a path:
Ping uses ICMP packets to measure reachability and round trip delay from a source host to a remote host.
Traceroute detects common reachability problems such as routing loops and network black holes by sending ICMP packets from a source host to a destination host, and by receiving ICMP responses from intermediate routers along the path between the source host and the remote host. Each intermediate router in the path decrements the TTL value stored in the header of an ICMP packet by one; when the TTL field expires (reaches the value zero) in a router, the router does not forward the packet towards the destination host. Instead, it returns the ICMP to the source host responding with a Time Exceeded response. By starting with an initial TTL value of 1 and gradually incrementing the TTL field in successive ICMP packets, the source host is able to receive an ICMP response from all the routers in the path. Traceroute also computes the round trip time of each ICMP packet, hence being able to determine the round trip delay between the source host and intermediate routers.
Pathchar measures congestion of a path by estimating performance characteristics of each node along a path from a source to a destination. Pathchar also leverages the ICMP protocol's Time Exceeded response to packets whose TTL has expired. By sending a series of UDP packets of various sizes to each hop, pathchar uses knowledge about earlier nodes and the round trip time distribution to this node to assess incremental bandwidth, latency, loss, and queue characteristics across the link connected to this node.
These tools are mainly used for troubleshooting purposes. A more formal attempt to measure performance characteristics of Internet paths is being developed by the IP Performance Metrics (IPPM) working group of the Internet Engineering Task Force (IETF). The IPPM working group has specified a general framework for measuring performance characteristics of a path, including specifications for clock synchronization and for size, number and inter-transmission time of measurement packets. The IPPM working group has also specified specific performance metrics for one-way delay, one-way inter-packet delay variation, and one-way loss, among others. The goal of the IPPM measurement framework is to allow service providers and other network providers to develop and operate and inter-operable measurement infrastructure, for performance and billing purposes, among other purposes.
However, even if this measurement infrastructure is in place, a way to communicate measurements and performance characteristics of measured paths to appropriate points of the network where decisions based on those performance characteristics can be made, is needed. In addition, this communication should be efficient, i.e., it should minimize the amount of bandwidth consumed.